Fly ash quality before and after conversion to low-No, combustion was investigated at a 150 MW unit in Kentucky burning a blend of western United States bituminous coal and Powder River Basin, WY, subbituminous coal. The fly ash collection system is divided into mechanical and baghouse collection systems. The mechanical collection hoppers, capturing fly ash from a hotter portion of the flue gas stream than the baghouse hoppers, tends to capture a coarser, carbon-rich fraction of the fly ash than the baghouse hoppers. The latter was particularly the case for the pre-conversion fly ash. The post-conversion fly ash had significantly more carbon than the pre-conversion ash. The post-conversion baghouse has abundant coarse, thin-walled carbon, suggesting that this particular carbon form is an artifact of the lower post-conversion combustion temperatures.